Semiconductor integrated circuit device

ABSTRACT

Using the leakage current of the base resistance of the bipolar transistor, semiconductor integrated circuit device which detects an overheat condition of the elements protected from overheat, is realized. The overheat detection circuit and the elements or the circuits which might be protected from overheat, are formed on the same substrate. 
     The said overheat detection circuit is comprised of a bipolar transistor, its base resistance, and a constant-voltage source. The constant-voltage source provides a certain voltage to isolate the elements. 
     The joint base resistance is located close to elements or circuits which might be protected from overheat and located far from the constant-voltage source.

This is a continuation of application Ser. No. 10/162,178 filed Jun. 5,2002 now U.S. Pat. No. 6,687,107; the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a semiconductor integrated circuitdevice such as semiconductor integrated circuit device, especiallyrelates to a semiconductor integrated circuit device on which aremounted elements or circuits possibly to overheat and on which ismounted also an overheat detection circuit.

BACKGROUND OF THE INVENTION

As an overheat detection circuit mounted on the integrated circuit,those circuits shown in the drawing FIG. 4A through FIG. 4C have beenknown. In FIG. 4A, the circuit utilizes a thermal characteristic ofdiode's forward voltage drop, which detects the temperature of a placewhere the diode is located, and the said circuit produces an overheatdetective signal when the temperature reaches a certain degree.

In FIG. 4B, an output is produced by the overheat detective signal inaccordance with the increase of the leakage current of the base openedtransistor, i.e. the increase of the backward current of the parasitediode between the base and the emitter indicated by dotted line.

Furthermore, in FIG. 4C, the overheat detection circuit senses thetemperature by using the thermal characteristic of the constant-currentsource 1 and bipolar transistor 3 through the base resistance 2, and atthe same time amplifies the detection current.

For that reason, this circuit is designed to flow the output current ofthe constant-current source 1 from the joint of the base 3 of thetransistor 3 and the base resistance 2 to the base resistance 2.

And the collector current of the bipolar transistor 3 is transformedinto the voltage signal by the pull-up resistance 4 and this voltagesignal goes through the buffer 5. Thus the overheat detection currentmight be produced. The base resistor 2 is usually formed by asemiconductor pattern and so forth, surrounded by the well region 2 awhich is clamped to the base 3 a of the transistor 3 in order to beisolated from the other circuit elements.

However, the above-said known overheat detection circuits used for thesemiconductor device has advantages and disadvantages at the same time.For example, both the circuit shown in FIG. 4A and the circuit shown inFIG. 4C have an advantage and a disadvantage. It is easy to define thetemperature freely to produce the detective signal, but it is difficultto match the transition into the overheat condition to what temperatureof the detection.

As to the circuit in FIG. 4B, an advantage, on one hand, to detectcorrectly the transition into the overheat conditions since the leakagecurrent changes rapidly in accordance with the overheat conditions. Onthe other hand, it is difficult to design a circuit to obtain the stableoperation.

As the circuit in FIG. 4C has a base resistance, it is practical to usethe circuit and it has an advantage to utilize the current amplificationof the transistor without further additional elements.

In considering the above-said problem, such an overheat detectioncircuit is requested as can detect correctly the transition into theoverheat condition and is easy to utilize. In replying to the request,one idea is to make react to the leakage current as in FIG. 4B,maintaining the advantage of the overheat detection circuit as in FIG.4C. Therefore, it is the technical problem to improve the detectioncircuit based on the circuit in FIG. 4C.

SUMMARY OF THE INVENTION

It is an object of the invention to realize the semiconductor integratedcircuit device which detects the overheat by way of the leakage currentof the base resistance of the transistor

The above mentioned object of the present is accomplished by using theleakage current of the base resistance of the bipolar transistor. It isan object of our invention to realize a semiconductor integrated circuitdevice which detects an overheat condition of the elements protectedfrom an overheat is realized. That is, the overheat detection circuit isformed on the same substrate where the elements or the circuits whichare protected from overheat are formed. The said overheat detectioncircuit comprises a bipolar transistor, its base resistance, and aconstant-voltage source. The said constant-voltage source provides acertain voltage necessary to isolate the elements. In comparison withthe prior art, overheat detection circuit in FIG. 4C, a constant-voltagesource is introduced, and the base resistance is clamped to the outputof the constant-voltage source.

In this semiconductor integrated circuit device, the leakage currentfrom the well region to the base resistance is detected. The leakagecurrent is stabilized by the constant-voltage source and is amplified bythe transistor. And the operation of the bipolar transistor isstabilized because of the base resistance.

According to this invention, a semiconductor integrated circuit device,which detects an overheat based on the leakage current of the baseresistance of the transistor, will be realized.

Another improvement is that in the above-mentioned device, the baseresistance is located close to an elements and circuits protected fromthe overheat and located far from the constant-voltage source.

In this way the temperature of an object protected from overheat can bedetected correctly based on the leakage current of the base resistance.

As the constant-voltage source which provide a certain voltage with thewell region is located far from the protected objects, theconstant-voltage source is not influenced by the thermal change causedby the overheat protected elements or circuits.

A certain voltage which contributes to a stabilization of the leakagecurrent, is not influenced by the undesired thermal change. Therefore anoverheat detection can be made correctly.

According to this second invention, a semiconductor integrated circuitdevice which can detect the overheat correctly based on the leakagecurrent of the base resistance of the transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is one of the embodiment of this invention, FIG. 1A being acircuit of the overheat detection circuit, and FIG. 1B being a frontview in longitudinal section, showing the overheat detection circuit ofthis invention;

FIG. 2 is a circuit of the whole device of this invention;

FIG. 3 is a drawing which describes the detection operation;

FIG. 4A through FIG. 4C are drawings showing a prior art overheatdetection circuit.

PREFERRED EMBODIMENT OF THE INVENTION

Now, an embodiment of the present invention will described withreference to drawings. FIG. 1 shows the fundamental structure, FIG. 1Abeing the overheat detection circuit, FIG. 1B being the longitudinalcross section of the region where the base resistance is formed. FIG. 2is the whole circuit of the device. The same number is used for theelements identical or relevant to those in the said prior art circuits.

This semiconductor integrated circuit device (in FIG. 2) has anone-chip-substrate 10. On this substrate an overheat detection circuit(2-6), an output-transistor 9 which is protected from the overheatcondition and a control circuit 8 which controls output transistor 9 inaccordance with the result of the overheat detection.

As two sets of the output transistor 9 and control circuits are mountedon the substrate, a detective signal distribution circuit 7 is providedin order to transmit overheat detective signal to both of the controlcircuits 8.

The overheat detection circuit (2-6) (in FIG. 1A) is provided with theNPN transistor 3. The base resistance 2 is connected to the base of thetransistor as an overheat detection element which uses leakage current.In order to use it in the grounded-emitter connection mode which ispractical to use, the transistor 3 is designed so that the base 3 a ofwhich is connected through the base resistance 2 to the ground GND, theemitter of which is connected to the ground GND, the collector of whichis connected through pull-up resistor 4 to the power supply line Vcc. Inaddition, in order to produce the detective signal, the heat detectioncircuit (2-6) consists of the said pull-up resistance 4 which transformsthe collector current into the voltage and of the buffer 5 having MOStransistor which may switch in accordance with the voltage.

In order to form the base resistance 2 in the overheat detection circuit(FIG. 1B), in case the substrate 10 is p-type, firstly n-type wellregion 2 a should be formed and then p-type spot having an appropriatedensity is formed in an appropriate width and length within the saidregion 2 a, so that the desired resistance and thermal characteristicare obtained.

The well region 2 a is connected to the constant-voltage source 6, inorder to isolate the base resistance 2 from other elements and circuitsand in order to supply the leakage current in a stable condition. Thus acertain voltage, which is higher than the base may reach, is supplied tothe well region 2 a. The joint between the constant-voltage source 6 andthe well region 2 a, is made closer to the node of the base 3 a and base2 than the node of ground GND and base resistance 2 so that most of theleakage current runs toward transistor 3. In addition, high precisionband-gap-voltage source and so forth is suitable for theconstant-voltage source 6, and other type voltage source may also beused.

The output transistor 9 and the control circuit 8 (FIG. 2) constitute apower source which supplies power of a certain voltage to an externalload. In that case the output transistor 9 is, for example, comprised ofpower elements such as MOS transistor. And the control circuit 8controls on-off switching operation of the transistor 9 or its analogoperation in accordance with the external input indicated and thefeedback signal not indicated.

Also this circuit 8 stops the transistor 9's operation on receiving theoverheat detective signal through the detective signal distributioncircuit 7 from the buffer 5.

The said distribution circuit 7 may be comprised of MOS transistors orof bipolar type elements and some other elements insofar as it transmitsthe buffer's output to the control circuit 8, matching the output of thebuffer 5 to the input of the control circuit 8.

Referring to the layout of the semiconductor integrated circuit device,the base resistor 2 and the bipolar transistor 3 may be located close toeach other, preferably in the middle of them. And the constant-voltagesupply source 6, the pull-up resistance 4 and the buffer 5 may belocated as far as possible from the output transistor 9 in order toavoid the influence of the heat produced by the transistor 9.

The mode and operation of the above said semiconductor integratedcircuit device will be described referring to the figures. FIG. 3describes the detection operation, especially describes the leakagecurrent in the overheat detection operation and the collector currentwhich amplifies the said leakage current.

In the normal operation mode, the current running in the base resistance2 which are made up of forward current and leakage current, are verysmall, so that the transistor 3 is off. As a result the detective signalthat is transmitted to the control circuit 8 through the buffer 5 andthe detective signal distribution circuit 7, is not significant, i.e.the detective signal does not affect the operation, or the saiddetective signal is not transmitted.

The external input signal controls the operation of the circuit 8.Therefore the control circuit 8 controls the output transistor 9 inaccordance with the external input signal, so that the transistor 9keeps the switching operation.

The temperature of the transistor 9 rises as the transistor 9 operates,and so does the temperature of the base resistance region 2.

And so does increase the leakage current running through well region 2 aand base resistance 2 from the constant-voltage source 6 to the groundGRD and to the base 3 a of the transistor 3 (2 dotted line in FIG. 3)

The leakage current which is run to the base 3 a is amplified by thefactor hfe (current amplification), and transformed into the collectorcurrent.

As the leakage current of the base resistance 2 made from semiconductorincreases rapidly when the temperature of the semiconductor deviceapproaches to the limit of operation, the temperature of the transistor9 approaches to the upper limit, a significant detective signal istransmitted through the pull-up resistance 4 and the buffer 5.

And the control circuit 8 forces the transistor 9 to stop the operation.

Thus when the output transistor 9 becomes overheated, the detectioncircuit (2-6) detects it and stops the operation of the transistor 9.

The stop continues until the temperature of the transistor 9 goes down.When the temperature goes down to the certain degree, the transmissionof the significant detective signal from the overheat detection circuit(2-6) stops and the operation of the transistor reopens.

In addition to the accurate detection of the overheat condition, in thenormal operation mode when the circuit does not detect the overheatcondition, the transistor 3 operates in a stable way since the base 3 aof the transistor 3 is grounded through the base resistance 2. So themalfunction caused by instantaneous change of power supply line Vcc andelectromagnetic noises coming from the exterior may be avoided. As aresult, undesirable cases do not occur where the normal operation isstopped by the transmission of the unfavorable detective signal

In the above said cases, the circuit has 2 output transistors 9 whichare protected from an overheat. It may have one or more than threetransistors.

And plural overheat detection circuits (2-6) may be used.

Moreover, transistor 3 may be PNP, not limited to the NPN transistor.Also, substrate 10 may be n-type, not limited to be p-type.

As for the p-type substrate 10, firstly p-type well region 2 a should beformed and within that region 2 a n-type base resistance 2 ofappropriate density should be formed. The buffer 5 and the outputtransistor 9 may be bipolar transistor or may be some other sort of theelements, not limited by the MOS transistor. And the circuit may consistof a plural elements, not limited by a sole element.

It is clear from the above description that in the first embodiment, bychanging the clamp point of the well region of the base resistance tothe constant-voltage source, semiconductor integrated circuit device isrealized, that can detect overheat based on the leakage current of thebase resistance of the transistor.

Moreover, in the second embodiment, by allocating the overheat detectioncircuit in the semiconductor integrated circuit device, the overheatdetection circuit semiconductor integrated circuit device is realized,that can detect more accurately overheat, based on the leakage currentof the base resistance of the transistor.

1. A semiconductor integrated circuit device comprising: a substrate anoverheat detection circuit formed on said substrate, and at least oneelement or circuit that is formed on the same substrate as said overheatdetection circuit and comprises an overheat protected element orcircuit, said overheat detection circuit comprising a bipolartransistor, a base resistance of said bipolar transistor, and aconstant-voltage source, said substrate having a well region formedtherein and said well region having said base resistance formed therein,said constant-voltage source being directly connected to said wellregion in order to isolate said base resistance from said at least onecircuit or element and thereby provides a stable voltage to said wellregion.
 2. A semiconductor integrated circuit device as defined in claim1, where said base resistance is located close to said at least oneoverheat protected element or circuit, and at the same time the constantvoltage source is located far from said at least one overheat protectedelement or circuit.
 3. The semiconductor integrated circuit device asdefined in claim 1, wherein said overheat detection circuit furthercomprises a pull up resistance coupled to said bipolar transistor and abuffer coupled to said base resistance and said bipolar transistor. 4.The semiconductor integrated circuit device as defined in claim 1,wherein a clamp point of the well region of said base resistance to theconstant-voltage source is made closer to the node of said base of thebipolar transistor and the base resistance than the node of ground andthe base resistance.
 5. The semiconductor integrated circuit device asdefined in claim 1, wherein said substrate comprises a plurality ofelements or circuits that are protected by said overheat detectioncircuit.
 6. The semiconductor integrated circuit device as defined inclaim 1, further comprising a control circuit formed on said substratefor said at least one overheat protected element or circuit.
 7. Thesemiconductor integrated circuit device as defined in claim 3, whereinsaid bipolar transistor is an NPN transistor.
 8. The semiconductorintegrated circuit device as defined in claim 3, wherein said bipolartransistor is a PNP transistor.
 9. The semiconductor integrated circuitdevice as defined in claim 1 comprising a plurality of said overheatdetection circuits and corresponding overheat protected elements orcircuits.
 10. The semiconductor integrated circuit device as defined inclaim 4, wherein a leakage current which is run to the base of saidtransistor is amplified and transformed into a collector current.